Optical fiber splice

ABSTRACT

An optical fiber splice comprising a hinged splice element having two legs, at least one of the legs having a groove therein for holding the fibers to be spliced, and an index matching gel disposed between the legs. In the embodiment wherein the legs remain divergent or slightly open in the clamping state, a vent hole is punched in the center of the splice element to minimize migration of the gel between the inner and outer surfaces of the elements near the fiber interface, which could otherwise increaase insertion loss due to the migration of microbubbles, particularly during temperature cycling. A vent channel may optionally be formed in the splice element to provide fluid communication between the groove and the vent hole. In the embodiment wherein the legs are essentially parallel and in intimate contact in the clamping state, rails may be provided in one leg opposite leg with the groove whereby the rails impinge on either side of the groove and block the flow of the index matching gel.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S patent applicationSer. No. 07/692,271 filed Apr. 26, 1991 now U.S. Pat. No. 5,102,212,which is a continuation of U.S. patent application Ser. No. 07/437,027filed on Nov. 15, 1989, now U.S. Pat. No. 5,013,123, which is acontinuation-in-part of U.S. patent application Ser. No. 07/305,471filed on Feb. 1, 1989, (abandoned), which is a continuation of U.S.patent application Ser. No. 07/182872 filed Apr. 18, 1988, now U.S. Pat.No. 4,824,197.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to devices for opticallysplicing waveguides such as optical fibers, and more particularly to avented, hinged splice element having improved hinge registration andclamping of the optical fiber.

2. Description of the Prior Art

Splices for optical fibers are known in the art. The most criticalcharacteristic of an optical fiber splice is its insertion loss, i.e.,the signal loss due to misalignment of the fibers, which may occur inthree different manners. First of all, the fiber end faces should abuteach other as closely as possible (end offset). The provision of arefractive index matching medium (gel) at the interface may mitigate theeffects of any air space left between the end faces. Secondly, the fiberaxes proximate the interface should be generally parallel, so that lightexiting one fiber will strike the surface of the second fiber as closelyas possible to a right angle, or 0° angle of incidence (axial or angularoffset). Finally, the axes of the fibers should be transversely alignedto maximize the overlapping surface area between the end faces (lateralor transverse offset). This alignment is critical since the diameter ofthe central glass core of single mode fibers is only about 8 μm, so adeviation in axial alignment of as little as 1 μm may result in asignificant loss.

Several prior art optical fiber splicing devices attempt to optimizefiber alignment by utilizing a chip or tray having one or more groovestherein which receive the optical fibers. See, e.g., U.S. Pat. Nos.3,864,018; 4,028,162; 4,046,454; 4,102,561; 4,220,397; 4,730,892; and4,865,413. The grooves in the substrate provide a simple method forholding the fibers, which are forcibly held in the grooves by acompression plate or adjacent groove tray, or by the use of adhesives.The grooves may be concave or V-shaped. Concave grooves result in twoprimary points of contact with the fiber, while a V-groove with anopposing flat surface provides three points of contact. V-grooves in twoopposing trays result in four points of contact, as shown in FIG. 4 ofU.S. Pat. No. 4,046,454.

Some prior art splices combine the V-groove concept with a foldable orhinged splice element. See, e.g., U.S. Pat. Nos. 4,029,390; 4,254,865;4,818,055; and 4,865,412; and Japanese Patent Applications (Kokai) Nos.53-26142 and 58-158621. This basic design offers several advantages,including ease of manufacture (via stamping), low insertion force(preventing buckling or deformation of the fibers), fiber retentionwithout the use of adhesives or epoxies, and reusability.

In spite of the foregoing achievements, however, the mass splicing offibers in a reliable, quick and economic fashion remains a problem. Forexample, prior art hinged splice elements do not always bend along thesame line on the splice element, and there is a high rejection rateduring production. Without precise folding of the element, parallel tothe fiber receiving grooves, fiber alignment and retention is affectedsince it results in inaccurate registration of the two halves of thesplice element, and is especially critical when the two halves havecomplimentary V-grooves. It has also been found that ductile hingeelements, such as that disclosed in U.S. Pat. No. 4,824,197 (not priorart), require an annealing step after embossing in order to provide ahinge which will consistently survive a 180° fold.

The sudden clamping transition near the fiber interface also causesdeformation of the fiber resulting in more signal loss than if therewere a more gradual clamping toward the interface.

Prior art optical splices also do not adequately address the optimumgeometry for V-groove designs. For example, in the previously referredto FIG. 4 of U.S. Pat. No. 4,046,454, the V-grooves have obtuse angles,meaning that the four points of contact will not be completelysymmetrical about the fiber. This may result in unnecessary transverseoffset of the fibers, leading to greater splice loss. This is also truefor hinged splice elements wherein a flat surface compresses the fiberinto a 60° V-groove. Since the flat surface is hinged to the groovedsurface, and since the fiber is only partially embedded in the groove,the flat surface is not parallel to the groove-bearing surface when thesplice element is in its closed, clamping state. See, e.g., U.S. Pat.No. 5,013,123 (this patent does not constitute prior art). Since thesetwo surfaces are not parallel, the three lines or surfaces contactingthe fiber will not be symmetrically positioned about the fiber, againadversely affecting transverse offset of the fiber end faces.

One final disadvantage relating to prior art optical splices concernsthe use of a medium for matching the index of refraction of the twofibers. As mentioned above, reflective losses may be minimized byplacing an index matching fluid or gel at the fiber interface.Oftentimes, however, this gel has bubbles, contaminants or otherdiscontinuities which tend to migrate during the splice operation, andthereafter with temperature cycling. Such migration of the gel andmicrobubbles can detrimentally affect the splice quality. It would,therefore, be desirable and advantageous to devise an optical spliceelement which would obviate any problems associated with gel migration,as well as overcome the aforementioned limitations regarding apredictable hinge fold line, optimum V-groove geometry, and gradualclamping of the splice element.

SUMMARY OF THE INVENTION

The foregoing objective is achieved in an optical splice elementcomprising a thin sheet of deformable material having on one surfacethereof a notched web forming a focus hinge connecting two leg portionsof the sheet, and providing an accurate and predictable fold line. Atleast one of the leg portions has a V-groove embossed therein, and theother of the leg portions has either another V-groove or a contactsurface positioned so as to lie adjacent the V-groove on the first legportion when the legs are folded toward one another along the fold linedefined by the longitudinal notch. Means are provided to gradually clampthe central portions of the legs to minimize insertion loss from asudden clamping transition.

Optimum V-groove geometry is achieved by offsetting the angle of theV-grooves with respect to the plane of the leg, or by offsetting theangle of the contact surface. The value of the interior angle of theV-groove(s) depends upon the number of points or lines which willcontact the fiber placed in the groove. This value may be decreasedslightly whereby, when the fiber is clamped between the legs and theductile surface of the V-groove deforms, the deformation results in aneffective angle corresponding to the desired optimum angle. A vent holeis provided at the center of the splice element to prevent migration ofmicrobubbles in the index matching gel across the fiber interface.Alternatively, sealing rails may be formed on one leg if the surfaces ofthe two legs are in intimate contact when the element is in a closed,clamping state.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features and scope of the invention are set forth in theappended claims. The invention itself, however, will best be understoodby reference to the accompanying drawings, wherein:

FIG. 1 is a top plan view of the splice element of the present inventionin its unfolded state;

FIG. 2 is a side elevational view of the splice element in its unfoldedstate, showing the focus hinge defined by a longitudinal notch;

FIG. 3 is a side elevational view of the splice element in its foldedstate, with a fiber disposed in the V-grooves;

FIGS. 4A and 4B are detail diagrams depicting the angular geometry ofthe V-grooves and contact surface;

FIG. 5 is a detail diagram illustrating the provision of a smallerV-groove angle to compensate for the deformation of the ductile surfaceof the V-groove, and also showing rails which provide sealing of theindex matching gel;

FIG. 6 is an exploded perspective view of the complete splice of thepresent invention, including the splice body and splice element;

FIG. 7 is a bottom plan view of the cap of the splice body of thepresent invention; and

FIG. 8 is a cross-section taken along the center of the closed splicedepicting clamping of the splice element.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference now to the figures, and in particular with reference toFIG. 1, there is depicted the optical fiber splice element 10 of thepresent invention. Splice element 10 is somewhat similar to the spliceelements described in U.S. Pat. Nos. 4,824,197 and 5,013,123, thedisclosures of which are hereby incorporated by reference. Spliceelement 10 is formed from a sheet 12 of deformable material, preferablya ductile metal such as aluminum, although polymeric materials may alsobe used, such as polyethersulfone. Material selection is describedfurther below. Although the term "connector" may be applied to spliceelement 10, that term is usually reserved for devices which are intendedto provide easy connection and disconnection, as opposed to a splicewhich is usually considered permanent. Nevertheless, the term "splice"should not be construed in a limiting sense since splice element 10 canindeed allow removal of the spliced fiber.

With further reference to FIG. 2, certain features of splice element 10are embossed, coined, stamped or molded into sheet 12. First of all, agroove 14 is formed on the outside surface 16 of sheet 12, extendinggenerally the length of sheet 12. Groove 14 is centrally located,forming an area of reduced thickness which defines a hinge thatseparates sheet 12 into two identical plate-like members or legs 18 and20. In one embodiment of the present invention, both of these legs haveV-shaped grooves 22 and 24 embossed on the inside surface 26 of sheet12. It should be noted that it is not necessary for the grooves to havea sharp angle in order to be considered V-shaped; given the smalldimensions involved, the apex of the "V" may be somewhat curved or evenflattened out, but the overall shape is still generally that of a "V."V-grooves 22 and 24 are generally parallel with groove 14, andequidistant therefrom, but do not extend the full length of sheet 12.Concave recesses 28 and 30 lie adjacent grooves 22 and 24, respectively,whereby, when legs 18 and 20 are folded together (as shown in FIG. 3),recesses 28 and 30 form a lead-in cone for an optical fiber 32.

A key feature of the present invention involves improvements in thehinge which provide a fold line allowing precise transverse registrationof V-grooves 22 and 24. The essential improvement in this regard is theprovision of another groove or notch 34 on surface 26, opposite groove14. Notch 34, which preferably takes the shape of a shallow "V," liesabove the centerline of groove 14. Empirical testing has shown thatprovision of such a focus hinge 35 provides more accurate registrationof legs 18 and 20 than if notch 34 were not present, to within about ±30μm (3 σ). Moreover, the registration is very predictable and repeatable,making the folding step non-critical. Focus hinge 35 may be utilized toregister any kind of groove, not only those that are V-shaped. Even ifonly one of the legs 18 or 20 had a groove therein, obviating the needfor alignment of opposing grooves, it would still be desirable to usefocus hinge 35 to provide optimum registration of recesses 28 and 30 inorder to form a proper lead-in cone.

The added predictability in the use of focus hinge 35 may be furtherenhanced by cutting or embossing groove 14 in such a manner as to form aconvex surface 36 on one side of the hinge web 38. This forms a partialbend radius at the hinge, and allows hinge web 38 to be thicker withouthampering the bending qualities. The increased thickness in turn impartsstructural integrity and, in testing, this hinge has survived fullclosing and reopening without failure. The splice elements shown in thepreviously mentioned U.S. Pat. Nos. 4,824,197 and 5,013,123 require onlya 90° bend at each hinge, but the hinge in splice element 10 mustsurvive a bend of nearly 180°; the splice elements shown in thosepatents require a post-embossing annealing step to survive such a fold,but this is not necessary with focus hinge 35.

Referring now to FIG. 3, optical fiber splice element 10 is depicted inits closed state, clamping a fiber 32 between V-grooves 22 and 24 oflegs 18 and 20. Splice element 10 may be preloaded in the folded state(although not in the closed, clamping state) in an optical spliceconnector body such as that shown in U.S. Pat. No. 4,818,055 (thedisclosure of which is hereby incorporated). Such a splice body includesa base and a cap. As the cap is moved from an open position to a closedposition, two cam bars slide over legs 18 and 20, urging them toward oneanother. It is desirous to provide rounded edges along outside surface16 of legs 18 and 20 to facilitate the camming action.

Sheet material 12 should be sufficiently deformable so as to partiallyconform to the surface of optical fiber 32 at the points of contact. Inaddition to improved signal transmission, this also results in greaterfiber retention and facilitates splicing of two fibers of differingdiameters. Sheet 12 may therefore be constructed from a variety ofductile metals, such as soft aluminum. The preferred metal is analuminum alloy conventionally known as "3003," having a temper of 0 anda hardness on the Brinnell scale (BHN) of between 23 and 32. Anotheracceptable alloy is referred to as "1100," and has a temper of 0, H14 orH15. Acceptable tensile strengths vary from 35 to 115 megapascals.

Other metals and alloys, or laminates thereof, may be used in theconstruction of sheet 12. Such metals include copper, tin, zinc, lead,indium, gold and alloys thereof. It may be desirable to provide atransparent splicing element to facilitate the splicing operation. Insuch a case, a clear polymeric material may be used for sheet 12.Suitable polymers include polyethylene terephthalate, polyethyleneterephthalate glycol, acetate, polycarbonate, polyethersulfone,polyetheretherketone, polyetherimide, polyvinylidene fluoride,polysulfone, and copolyesters such as VIVAK (a trademark of SheffieldPlastics, Inc., of Sheffield, Mass).

As an alternative to providing a sheet constructed of a deformablematerial, sheet 12 may instead be constructed of a more rigid materialprovided that the V-grooves and contact surfaces are lined or coatedwith a deformable material. The primary requisite is to provide amaterial which is softer than the glass comprising the optical fiber andcladding, and which is ductile under the clamping pressures applied tothe optical fiber. It is also desirable that the material be elastic atlow stress levels to afford sufficient elasticity to maintain acontinual compressive force on the optical fibers once legs 18 and 20have been brought together. Furthermore, a coating may be applied to theductile material to reduce skiving of the material as the fiber isinserted. For example, an obdurate coating having a thickness in therange of one to two μm may be applied to surface 26 of splice element10.

The dimensions of sheet 12 may vary considerably depending upon theapplication; the following dimensions are considered exemplary and arenot to be construed in a limiting sense. The size of sheet 12 is about18 mm long by 8 mm wide along the major edges. For both metal andpolymeric materials, the preferred thickness is about 0.51 mm. The widthof notch 34 is about 0.56 mm while its maximum depth, measured fromsurface 26, is about 0.1 mm. The width of groove 14 is approximately 1.1mm measured across surface 16, and 0.46 mm measured across hinge web 38;its maximum depth, measured from surface 16, is about 0.33 mm. Convexsurface 36 has a radius of curvature of about 0.39 mm. Based on theforegoing values, V-grooves 22 and 24 are preferably placed about 0.9 mmfrom the fold line defined by notch 34. V-grooves 22 and 24 should havea maximum width of about 129 μm.

FIGS. 4A and 4B illustrate the novel angular geometries of the V-groovesused in splice element 10. As noted in the Description of the Prior Art,prior art splices having V-grooves do not clamp the fiber in acompletely symmetrical fashion, resulting in unnecessary fiberdeformation and greater splice loss. Splice element 10, in contrast,optimizes the radial alignment of forces impacting the fiber bycounterbalancing the locations of the splice-fiber interfaces. In spliceelement 10, where the legs 18 and 20 are still separated by a smallangle in the closed, clamping state, this is accomplished by offsettingthe V-groove angles with respect to the plane of surface 26.

In FIG. 4A, V-grooves 22 and 24 have interior right angles, but theangles α and β are not equal. Rather, they are chosen to complement theangular separation of legs 18 and 20. Specifically, in the embodimentwhere legs 18 and 20 are separated by an angle γ of about 6° in theclosed, clamping state, the angles α are about 138°, i.e, thesupplementary angles of inclination are about 42°. The angles β areaccordingly about 132°, i.e., the supplementary angles of inclinationare about 48°. It can be seen that these angles (for two opposingV-grooves) are determined by the equations α=135°+γ/2, and β=135°-γ/2.It would, of course, be equivalent to make both angles of inclination ofone V-groove 45° and provide the angular offset in the second V-groove,i.e., making its angle α=135°+γ, and its angle β=135°-γ.

In the embodiment of FIG. 4B (which is presently considered to be thepreferred embodiment), there is only one V-groove 40 with an interiorangle of 60° (and angles of inclination with respect to surface 26 alsoof 60°). A complementary contact surface 42 is provided which has anangular offset δ with respect to surface 26 (contact surface 42 is thus"groove" as that term is used in the claims). The angle δ is simply180°-γ (γ is again preferably 6°). Another way of expressing theseconstructions is that, even though the two surfaces 26 are not parallel,the points of contact between splice element 10 and fiber 32 form anessentially regular polygon, such as the square 44 in FIG. 4A and theequilateral triangle 46 in FIG. 4B. The basic principle of offsettingthe angular geometries of the grooves may also be applied to spliceshaving more than four contact points. Focus hinge 35 also enhances theusability of such multiple surface clamps, as well as grooves having asemicircular cross-section. Optimizing these geometries also providesimproved alignment of different sized fibers.

Upon reference to the description provided herein, those skilled in theart will appreciate that, since the optical fiber may become slightlyembedded in a groove formed of a ductile material, it may be desirableto provide an initial groove angle slightly less than that ultimatelydesired for symmetric alignment of the fiber within the groove. Forexample, if splice element 10 uses two opposing V-grooves as shown inFIG. 4A, the interior groove angles should actually be slightly lessthan 90°. In this manner, when the fiber is clamped between legs 18 and20, the ductile material along the surfaces of V-grooves 22 and 24 willdeform at the points of contact with fiber 32, yielding an effectiveangle of about 90°. In this regard, the term "effective angle" refers tothat angle defined by the apex of the V-groove and the points of maximumdeformation of the ductile material where it contacts the fiber.Similarly, if the splice utilizes only one V-groove, as shown in FIG.4B, the interior angle should be slightly less than 60°.

This is further depicted in FIG. 5, which shows a splice element whereinthe inner surfaces of the legs are essentially parallel when the elementis in the closed clamping state. FIG. 5 illustrates the deformation ofthe V-groove surfaces, and how the initial angle formed in the V-groovediffers from the effective angle which is indicated by dashed lines 47.While the value of the interior V-groove angle depends primarily on theamount of ductile material which is displaced, this in turn depends uponthe malleability of the material comprising the surfaces of the V-grooveand the driving force which urges fiber 32 into the V-groove. Since awide variety of materials may be used for splice element 10, and sincethere are several different mechanisms for applying the clamping forceto the element, it is impossible to provide a single value for theinterior angle which will result in an optimum effective angle. In thepreferred embodiment of FIG. 4B, utilizing the clamping cap describedbelow, an angle in the range of 46°-59° has been empirically found toapproximately yield the optimum effective V-groove angle of 60°.

Referring back to FIG. 1, splice element 10 preferably has a gel 48disposed therein which has an appropriate index of refraction to improvetransmission of light across the fiber-to-fiber interface. Such gels areconventionally available. As noted in the Description of the Prior Art,the use of such a gel may result in the detrimental migration ofmicrobubbles or other contaminants along the fiber-to-fiber interface.Such migration may be arrested by the provision of a vent hole 50 nearthe center of splice element 10. Venting the area below focus hinge 35,adjacent the fiber interface, eliminates the pressure differential whichwould otherwise cause gel migration across the interface, particularlyduring temperature cycling. Vent hole 50 may be punched into sheet 12when splice element 10 is cut out; subsequent embossing of the variousgrooves and notches typically results in an hourglass shape of vent hole50. In the preferred embodiment, vent hole 50 has a diameter of about0.76 mm. A longitudinal vent channel 51 may optionally be embossed insurface 26 between vent hole 50 and grooves 22 and 24 to provide fluidcommunication between vent hole 50 and the grooves.

As an alternative to providing a vent hole, means may be provided toblock the flow of the index matching gel, such as providing a barrier oneither side of the V-groove proximate the fiber interface, rather thanpreventing the flow by eliminating any pressure differentials. Forexample, in the embodiment of FIG. 5, wherein the inner surfaces of thelegs are in intimate contact when the element is in the closed, clampingstate, features may be formed in one or both of the legs to providingsealing around the V-groove. One such means is a pair of ribs or rails52 formed on the surface of one of the legs. Thus, when the element isclosed, rails 52 impinge on the opposing surface, causing slightdeformation thereof, and provide an environmental seal which preventsgel migration near the fiber interface.

Turning to FIGS. 6-8, those figures depict the novel splice body 56which is used to hold and actuate splice element 10. Splice body 56 isessentially identical to the splice body described in U.S. Pat. No.4,818,055, except for the provision of a gradual or centralized clampingcam as discussed further below. Splice body 56 includes a cap member 58and a base member 60. Base 60 has an opening or central cavity 62therein for receiving splice element 10, and two side cavities 64 forreceiving locking tabs 66 of cap 58. Locking tabs 66 securely attach capmember 58 to base member 60. The end walls of base 60 further have holes68 therein which allow the insertion of the optical fiber into thepreassembled splice.

In addition to locking tabs 66, cap 58 also has two generally parallelcamming bars 70 which extend perpendicularly into cavity 62 and surroundsplice element 10. Locking tabs 66 and camming bars 70 are preferablyintegrally molded with cap member 58. In the preassembled state, cap 58is not fully inserted into base 60, allowing element 10 to remain in aslightly opened state, with the legs diverging, facilitating insertionof the optical fiber into the V-grooves thereof. Then, as cap 58 isforced fully into base 60, camming bars 70 forcibly contact legs 18 and20 of element 10, forcing them towards one another and clamping theoptical fiber.

The improvement in splice body 56 lies in the gradual thickening of thecamming surfaces 72 of camming bars near their center, as with cammingbar 70a shown in FIG. 7, which is a bottom plan view of cap 58. Thecross-section of FIG. 8 is taken at the center of the actuated splice,and additionally illustrates how camming bars 70 are thinner at theirdistal edges 76 than at the point of attachment to upper plate 74. Inother words, camming bar 70a defines an inwardly facing convex surface72 where it joins the upper plate 74 of cap member 58. Alternatively,the camming bars may be much shorter in length than splice element 10,such as camming bar 70b. In this manner, element 10 is allowed to flexopen at its ends, and there is a gradual clamping of the fiber towardsthe center. Both of these constructions have been found to decreaseinsertion loss associated with the microbends or deformations of thefiber which are found in other optical fiber splices. If camming barssuch as 70a are used, they are preferably about 18 mm long, and theminimum distance between the bars, at their center, is about 1.3 mm. Itis understood that gradual clamping may also be achieved if only one ofthe camming bars is so curved or thickened, the other having a flatinwardly facing surface. In the preferred embodiment, however, cammingbars such as 70b are used and are about 6.4 mm long, again with adistance between the bars of about 1.3 mm. The improved camming bars 70aand 70b may be used with splice element 10, or with the splice elementshown in U.S. Pat. No. 4,818,055, or with other splice elementsrequiring the clamping of two opposing legs or plate-like members.

Although the invention has been described with reference to specificembodiments, this description is not meant to be construed in a limitingsense. Various modifications of the disclosed embodiment, as well asalternative embodiments of the invention, will become apparent topersons skilled in the art upon reference to the description of theinvention. For example, splice element 10 may be provided with tabssimilar to that shown in U.S. Pat. No. 4,824,197 for securing theelement in a closed state. Splice element 10 may also contain multiplegrooves for splicing more than one fiber pair. It is thereforecontemplated that the appended claims will cover such modifications thatfall within the true scope of the invention.

I claim:
 1. An article for splicing two optical fibers together,comprising:a splice element having a hinge defining first and secondgenerally planar leg members, said splice element and leg members havinginside and outside surfaces; said first and second leg members havingmeans for holding a fiber therebetween; refractive index matching meansdisposed on said inside surfaces of said first and second leg members;and means for minimizing migration of said refractive index matchingmeans near an interface between the fibers.
 2. The article of claim 1wherein said means for minimizing migration of said refractive indexmatching means comprises a vent hole through said splice element, saidvent hole minimizing pressure differentials between said inside surfaceand said outside surface of said splice element.
 3. The article of claim1 wherein:said means for holding a fiber between said first and secondleg members comprises at least one groove formed in said inside surfaceof one of said leg members; and said means for minimizing migration ofsaid refractive index matching means comprises a vent hole through saidsplice element proximate said groove.
 4. The article of claim 1 whereinsaid refractive index matching means comprises a gel which is placed insaid splice element along said inside surface thereof.
 5. The article ofclaim 1 wherein said vent hole extends through said hinge of said spliceelement.
 6. The article of claim 2 wherein said vent hole is in thecenter of said splice element.
 7. The article of claim 3 wherein saidsplice element further has a vent channel formed therein providing fluidcommunication between said vent hole and said groove.
 8. The article ofclaim 4 wherein said means for minimizing migration of said refractiveindex matching means comprises means for blocking flow of said gelaround the fiber interface.
 9. The article of claim 8 wherein:said firstand second leg members are generally parallel when clamping the fibers;and said means for blocking flow of said gel comprises rail meansattached to said inner surface of one of said leg members proximate thefiber interface.
 10. The article of claim 9 wherein:said means forholding a fiber between said first and second leg members comprises agroove formed in said inside surface of said first leg member; and saidrail means comprises first and second rails formed on said insidesurface of said second leg member, said rails being generally parallelwith said groove and positioned on said inner surface of said second legmember whereby, when said first and second leg members are in a clampingstate, said rails forcibly impinge on said inner surface of said firstleg member on either side of said groove, providing an environmentalseal.
 11. An article for splicing two optical fibers together,comprising:a splice element having a hinge defining first and secondgenerally planar legs, said splice element and legs having inside andoutside surfaces; said first and second legs having means for holding afiber therebetween; refractive index matching gel disposed on saidinside surfaces of said first and second legs; and means for minimizingpressure differentials between said inner and outer surfaces of saidsplice element proximate an interface between the fibers.
 12. Thearticle of claim 11 wherein:said means for holding a fiber between saidfirst and second legs comprises at least one groove formed in saidinside surface of one of said legs; and said means for minimizingpressure differentials comprises a vent hole through said splice elementproximate said groove.
 13. The article of claim 11 wherein said venthole extends through said hinge of said splice element.
 14. The articleof claim 12 wherein said splice element further has a vent channelformed therein providing fluid communication between said vent hole andsaid groove.
 15. The article of claim 13 wherein said vent hole is inthe center of said splice element.
 16. An article for splicing twooptical fibers together, comprising:a ductile splice element having ahinge defining first and second generally planar legs, said spliceelement and legs having inside and outside surfaces; said first andsecond legs having means for holding a fiber therebetween; refractiveindex matching gel disposed on said inside surfaces of said first andsecond legs; and means providing a barrier to flow of said gel on eitherside of said holding means proximate the fiber interface.
 17. Thearticle of claim 16 wherein:said first and second legs are generallyparallel when clamping the fibers; and said means providing a barrier toflow of said gel comprises rail means attached to said inner surface ofone of said legs proximate the fiber interface.
 18. The article of claim17 wherein:said means for holding a fiber between said first and secondlegs comprises a groove formed in said inside surface of said first leg;and said rail means comprises first and second rails formed on saidinside surface of said second leg, said rails being generally parallelwith said groove and positioned on said inner surface of said second legwhereby, when said first and second leg members are in a clamping state,said rails forcibly impinge on said inner surface of said first legmember on either side of said groove.